1. Field of the Invention
The present invention relates generally to a lens drive mechanism of a camera, and more particularly to a lens drive mechanism of an auto-focusing camera.
2. Description of Related Art
Usually we need a camera to record the memorable moments. The designs of cameras have evolved toward lightweight and compactness, so have the currently popular digital cameras. Conventionally, an auto focus structure is used for controlling the telescopic movement of a lens of the camera.
The auto focus structure of the camera focuses on an object by comparing with the image on an image sensor. The image sensor is either a charge coupled device (CCD) sensor or a complementary metal oxide semiconductor (CMOS) sensor, and is controlled by a central processing unit (CPU) installed inside the digital camera. In the beginning, the lens moves back and forth around its original position (static position). As the lens moves, the CPU compares the image from the lens with the image in the image sensor. Finally, as the lens moves to the position where the image is the clearest, then the lens stops at the position. In this case, the lens has to be continuously driven back and forth by an annular cam. The annular cam is provided with a lens driving structure and driven to rotate by a stepping motor. At the moment when the CPU detects the clearest image as the lens moves back and forth, a stop signal is simultaneously sent to the lens. Therefore, the lens stops at the best focal position (static position). When the lens is to be moved back to the original position, the annular cam starts to rotate again. Once the lens moves back to its original position, the photo interrupter installed by the lens cylinder uses the shutter at the border of the lens cylinder to detect the original position of the lens. The shutter will interrupt the light of the penetration-type photo interrupter. The lens stops at the moment when the photo interrupter detects the original position.
Consequently, the lens in a digital camera auto focus system has to be driven continuously, so is the image detection. Every time an image is captured, the lens has to return to its original position. This method of searching for an optimal focal point makes use of mechanical and continuous lens motion to repeatedly check the image. Thus, the lens focusing procedure is very time-consuming, which, in most of cases, results in losing the best image-capturing time.